1. Field of the Invention
The present invention relates to a semiconductor light-emitting element, and in particular to a nitride-based compound semiconductor light-emitting element capable of emitting light with wavelengths ranging from a blue region to an ultraviolet region. The present invention also relates to a method for producing such a semiconductor light-emitting element.
2. Description of the Related Art
It is known that a nitride-based compound can be used in a semiconductor light-emitting element capable of emitting light with wavelengths ranging from a blue region to an ultraviolet region. For example, Japanese Laid-Open Patent Publication No. 11-177142 discloses a structure of a conventional nitride-based compound semiconductor light-emitting element using a nitride-based compound.
FIG. 9 is a cross-sectional view of a conventional nitride-based compound semiconductor light-emitting element 90 when viewed from the front. The nitride-based compound semiconductor light-emitting element 90 includes: a silicon (Si) substrate 95 having an N-type electrode 98 formed on the bottom surface thereof; a buffer layer 94 on the Si substrate 95; a lower cladding layer 93 on the buffer layer 94; a light-emitting layer 92 on the lower cladding layer 93; and an upper cladding layer 91 on the light-emitting layer 92. The upper cladding layer 91 includes a p-type pad electrode 96 for injecting current into the light-emitting layer 92 on a substantial center portion of the upper cladding layer 91. A gold (Au) conductor wire 97 for externally supplying current to the P-type pad electrode 96 is bonded to the top surface of the p-type pad electrode 96.
In the nitride-based compound semiconductor light-emitting element 90 having the above structure, since the P-type pad electrode 96 is directly formed on the upper cladding layer 91, there is a possibility that any crack might be caused in the upper cladding layer 91 by stress generated in the upper cladding layer 91 when forming the P-type pad electrode 96.
Further, there is a possibility that any crack might be caused to the upper cladding layer 91 by mechanical damage caused to the upper cladding layer 91 when bonding the Au conductor wire 97 to the top surface of the P-type pad electrode 96.
When any crack is caused to the upper cladding layer 91, current flows into the upper cladding layer 91 through the crack, and therefore the nitride-based compound semiconductor light-emitting element 90 is electrically shorted. As a result, there arises a problem that the light-emitting layer 92 might not emit light or might not stably emit light even if the light-emitting layer 92 can emit light.
Furthermore, about 50% of light emitted by the light-emitting layer 92 is absorbed into the Si substrate 95, and therefore there arises a problem that the luminous efficiency of the nitride-based compound semiconductor light-emitting element 90 might be reduced.